When the packet data service in a wireless communications system is active, resources in the infrastructure, e.g., base station transceiver subsystem (BTS), base station controller (BSC), packet control function (PCF), and the radio link are actively assigned to the participating communication devices. After a period of inactivity in a communication device, the corresponding traffic channel may transition to a dormant packet data session to conserve system capacity, reduce service cost, and save battery life. However, the act of transitioning the dormant packet data session back to an active packet data session is accompanied by a considerable delay in the system response. Existing wireless communication infrastructures provide limited opportunities for significantly reducing the latency in waking up a dormant packet data session, i.e., it is not possible to reduce the actual latency below the time that is required to re-establish the traffic channel for the dormant packet-data session.
For example, a class of wireless services intended for quick, efficient, one-to-one or one-to-many (group) communication has existed in various forms for many years. In general, these services have been half-duplex, where a user presses a “push-to-talk” (PTT) button on a phone/radio to initiate a group communication. If granted the floor, the talker then generally speaks for a few seconds. After the talker releases the PTT button, other users who are available may request the floor. These services have traditionally been used in applications where one person, a “dispatcher,” needs to communicate with a group of people, such as field service personnel or taxi drivers, which is where the “dispatch” name for the service comes from. Similar services have been offered on the Internet and are generally known as “voice chat.”
A key feature of these services is that communication is quick and spontaneous, usually initiated by simply pressing a PTT button, without going through a typical dialing and ringing sequence. Communication in this type of service is generally very short, with individual talk “spurts” being generally on the order of several seconds, and “conversations” lasting possibly a minute or less. The time delay between when the user requests the floor and when the user receives a positive or negative confirmation from a group communication server indicating that the user has the floor and may begin speaking is known as PTT latency.
PTT latency is a critical parameter for half-duplex group communications systems. As mentioned previously, dispatch services place a priority on short, quick conversations, which makes the service less attractive if PTT latency becomes large.
There is a need, therefore, for mechanisms to reduce the effect of PTT latency as perceived by the talker and to make the talker to attribute the undesirable system latency to the target users rather than to the system or the service provider.